1. Field of the Invention
The present invention relates in general to an input/output terminal circuit for a system such as a video cassette recorder, and more particularly to an automatic input/output terminal varying circuit for automatically varying input/output terminals to output terminals and input terminals, respectively, in accordance with a user's input signal selection so that the usefulness of the input/output terminals can be increased.
2. Description of the Prior Art
Referring to FIG. 1, there is shown a circuit diagram of a conventional signal input/output terminal circuit. As shown in this drawing, the signal input/output terminal circuit comprises an input/output terminal section 1 for inputting external video signals and external right and left audio signals and outputting a video signal and right and left audio signals. The input/output terminal section 1 has a plurality of sets of a video terminal V and two audio terminals R and L. A signal selection section 2 is provided to select one of the input video and audio signal sets from the input/output terminal section 1 and a television (TV) signal from a tuner in response to select data D0 and D1 from a microcomputer 4 and output, the selected signals to a signal processor 3 is noted herein that the TV signal includes a set of a video signal and right and left audio signals.
FIG. 1, the input/output terminal section 1 is shown to have two sets of input terminals A (V1, R1 and L1 ) and B (V2, R2 and L2) and a set of output terminals C (V3, R3 and L3). Also, the signal selection section 2 includes a select switch SW1 for selecting one of the input video and audio signal sets from the input/output terminal section 1 and the TV signal from the tuner and outputting the selected signals to the signal processor 3 and a switch controller 2a for generating a select control signal to the select switch SW1 in response to the select data D0 and D1 from the microcomputer 4. The select switch SW1 and the switch controller 2a are arranged on a single chip. The signal output terminals C in the input/output terminal section 1 are connected directly to an signal output line of the select switch SW1 to output the selected signals from the selects switch SW1 externally.
The operation of the conventional signal input/output terminal circuits with the above-mentioned construction will hereinafter be described.
First, the video signals V and the audio signals R and L from external signal sources (not shown) are inputted through the input terminals A and B in the input/output terminal section 1 and then applied to fixed terminals a and b of the select switch SW1 in the signal selection section 2. Also, the TV signal is applied to a fixed terminal t of the select switch SW1. At this time, when the user selects one of the inputted signals using a keyboard (not shown) or a select switch (not shown) to watch it the microcomputer 4 generates the select data D0 and D1 to the signal selection section 2 according to the user's selection.
The switch controller 2a controls the selection of the select switch SW1 in response to the select data D0 and D1 from the microcomputer 4. Under the control of the switch controller 2a, the select switch SW1 selects a set of the video signal V and the audio signals R and L of one of the input signal s through the input terminals A and B in the input/output terminal section 1 and the TV signal from the tuner. Then, the select switch SW1 outputs the selected signals to the signal processor 3 and through the output terminals C in the input/output terminal section 1 to an external system.
However, the conventional signal input/output terminal circuit has a disadvantage, in that the input/output terminals can perform only their specified input/output functions. Namely, the input terminals not used presently cannot be used for the output function and the output terminals not used presently cannot be used for the input function. This results in an increase in the number of the input/output terminals when the input and output signals are desired above a predetermined number. In this case, the input/output terminal section possesses a larger area and the usefulness of the input/output terminals are reduced.